/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_biquad_cascade_df1_fast_q15.c
*
* Description:	Fast processing function for the
*				Q15 Biquad cascade filter.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
*
* Version 0.0.9  2010/08/16
*    Initial version
*
*
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup BiquadCascadeDF1
 * @{
 */

/**
 * @details
 * @param[in]  *S points to an instance of the Q15 Biquad cascade structure.
 * @param[in]  *pSrc points to the block of input data.
 * @param[out] *pDst points to the block of output data.
 * @param[in]  blockSize number of samples to process per call.
 * @return none.
 *
 * <b>Scaling and Overflow Behavior:</b>
 * \par
 * This fast version uses a 32-bit accumulator with 2.30 format.
 * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
 * Thus, if the accumulator result overflows it wraps around and distorts the result.
 * In order to avoid overflows completely the input signal must be scaled down by two bits and lie in the range [-0.25 +0.25).
 * The 2.30 accumulator is then shifted by <code>postShift</code> bits and the result truncated to 1.15 format by discarding the low 16 bits.
 *
 * \par
 * Refer to the function <code>arm_biquad_cascade_df1_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.  Both the slow and the fast versions use the same instance structure.
 * Use the function <code>arm_biquad_cascade_df1_init_q15()</code> to initialize the filter structure.
 *
 */

void arm_biquad_cascade_df1_fast_q15(
    const arm_biquad_casd_df1_inst_q15* S,
    q15_t* pSrc,
    q15_t* pDst,
    uint32_t blockSize)
{
	q15_t* pIn = pSrc;                             /*  Source pointer                               */
	q15_t* pOut = pDst;                            /*  Destination pointer                          */
	q31_t in;                                      /*  Temporary variable to hold input value       */
	q31_t out;                                     /*  Temporary variable to hold output value      */
	q31_t b0;                                      /*  Temporary variable to hold bo value          */
	q31_t b1, a1;                                  /*  Filter coefficients                          */
	q31_t state_in, state_out;                     /*  Filter state variables                       */
	q31_t acc;                                     /*  Accumulator                                  */
	int32_t shift = (int32_t)(15 - S->postShift);  /*  Post shift                                   */
	q15_t* pState = S->pState;                     /*  State pointer                                */
	q15_t* pCoeffs = S->pCoeffs;                   /*  Coefficient pointer                          */
	uint32_t sample, stage = S->numStages;         /*  Stage loop counter                           */



	do {

		/* Read the b0 and 0 coefficients using SIMD  */
		b0 = *__SIMD32(pCoeffs)++;

		/* Read the b1 and b2 coefficients using SIMD */
		b1 = *__SIMD32(pCoeffs)++;

		/* Read the a1 and a2 coefficients using SIMD */
		a1 = *__SIMD32(pCoeffs)++;

		/* Read the input state values from the state buffer:  x[n-1], x[n-2] */
		state_in = *__SIMD32(pState)++;

		/* Read the output state values from the state buffer:  y[n-1], y[n-2] */
		state_out = *__SIMD32(pState)--;

		/* Apply loop unrolling and compute 2 output values simultaneously. */
		/*      The variable acc hold output values that are being computed:
		 *
		 *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
		 *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
		 */
		sample = blockSize >> 1u;

		/* First part of the processing with loop unrolling.  Compute 2 outputs at a time.
		 ** a second loop below computes the remaining 1 sample. */
		while(sample > 0u) {

			/* Read the input */
			in = *__SIMD32(pIn)++;

			/* out =  b0 * x[n] + 0 * 0 */
			out = __SMUAD(b0, in);
			/* acc =  b1 * x[n-1] + acc +=  b2 * x[n-2] + out */
			acc = __SMLAD(b1, state_in, out);
			/* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
			acc = __SMLAD(a1, state_out, acc);

			/* The result is converted from 3.29 to 1.31 and then saturation is applied */
			out = __SSAT((acc >> shift), 16);

			/* Every time after the output is computed state should be updated. */
			/* The states should be updated as:  */
			/* Xn2 = Xn1    */
			/* Xn1 = Xn     */
			/* Yn2 = Yn1    */
			/* Yn1 = acc   */
			/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
			/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */

#ifndef  ARM_MATH_BIG_ENDIAN

			state_in = __PKHBT(in, state_in, 16);
			state_out = __PKHBT(out, state_out, 16);

#else

			state_in = __PKHBT(state_in >> 16, (in >> 16), 16);
			state_out = __PKHBT(state_out >> 16, (out), 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */

			/* out =  b0 * x[n] + 0 * 0 */
			out = __SMUADX(b0, in);
			/* acc0 =  b1 * x[n-1] , acc0 +=  b2 * x[n-2] + out */
			acc = __SMLAD(b1, state_in, out);
			/* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
			acc = __SMLAD(a1, state_out, acc);

			/* The result is converted from 3.29 to 1.31 and then saturation is applied */
			out = __SSAT((acc >> shift), 16);


			/* Store the output in the destination buffer. */

#ifndef  ARM_MATH_BIG_ENDIAN

			*__SIMD32(pOut)++ = __PKHBT(state_out, out, 16);

#else

			*__SIMD32(pOut)++ = __PKHBT(out, state_out >> 16, 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */

			/* Every time after the output is computed state should be updated. */
			/* The states should be updated as:  */
			/* Xn2 = Xn1    */
			/* Xn1 = Xn     */
			/* Yn2 = Yn1    */
			/* Yn1 = acc   */
			/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
			/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */

#ifndef  ARM_MATH_BIG_ENDIAN

			state_in = __PKHBT(in >> 16, state_in, 16);
			state_out = __PKHBT(out, state_out, 16);

#else

			state_in = __PKHBT(state_in >> 16, in, 16);
			state_out = __PKHBT(state_out >> 16, out, 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */


			/* Decrement the loop counter */
			sample--;

		}

		/* If the blockSize is not a multiple of 2, compute any remaining output samples here.
		 ** No loop unrolling is used. */

		if((blockSize & 0x1u) != 0u) {
			/* Read the input */
			in = *pIn++;

			/* out =  b0 * x[n] + 0 * 0 */

#ifndef  ARM_MATH_BIG_ENDIAN

			out = __SMUAD(b0, in);

#else

			out = __SMUADX(b0, in);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */

			/* acc =  b1 * x[n-1], acc +=  b2 * x[n-2] + out */
			acc = __SMLAD(b1, state_in, out);
			/* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
			acc = __SMLAD(a1, state_out, acc);

			/* The result is converted from 3.29 to 1.31 and then saturation is applied */
			out = __SSAT((acc >> shift), 16);

			/* Store the output in the destination buffer. */
			*pOut++ = (q15_t) out;

			/* Every time after the output is computed state should be updated. */
			/* The states should be updated as:  */
			/* Xn2 = Xn1    */
			/* Xn1 = Xn     */
			/* Yn2 = Yn1    */
			/* Yn1 = acc   */
			/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
			/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */

#ifndef  ARM_MATH_BIG_ENDIAN

			state_in = __PKHBT(in, state_in, 16);
			state_out = __PKHBT(out, state_out, 16);

#else

			state_in = __PKHBT(state_in >> 16, in, 16);
			state_out = __PKHBT(state_out >> 16, out, 16);

#endif /*   #ifndef  ARM_MATH_BIG_ENDIAN    */

		}

		/*  The first stage goes from the input buffer to the output buffer.  */
		/*  Subsequent (numStages - 1) occur in-place in the output buffer  */
		pIn = pDst;

		/* Reset the output pointer */
		pOut = pDst;

		/*  Store the updated state variables back into the state array */
		*__SIMD32(pState)++ = state_in;
		*__SIMD32(pState)++ = state_out;


		/* Decrement the loop counter */
		stage--;

	} while(stage > 0u);
}


/**
 * @} end of BiquadCascadeDF1 group
 */
